Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$122.71	9.485%	$134.349	$134.35	$134.35	$134.30
Purchase #2	$244.94	6.873%	$261.7747	$261.77	$261.75	$261.80
Purchase #3	$186.48	7.640%	$200.7271	$200.73	$200.75	$200.70
Purchase #4	$215.94	10.582%	$238.7908	$238.79	$238.80	$238.80
Purchase #5	$58.35	5.470%	$61.5417	$61.54	$61.55	$61.50
Purchase #6	$249.58	12.535%	$280.8649	$280.86	$280.85	$280.90
Purchase #7	$227.69	12.619%	$256.4222	$256.42	$256.40	$256.40
7 purchase totals =	$1,305.69		$1,434.4704	$1,434.46	$1,434.45	$1,434.40